DESCRIPTION: (Investigator's abstract): The electroretinogram, ERG, is currently a valuable noninvasive technique available for diagnosing and following the course of retinal diseases. It has recently been shown that the initial portion of the human ERG can provide a quantitative measure of human rod receptor activity (Hood & Birch, 1990). These findings suggest that the ERG can be employed to answer fundamental questions about the functioning of both normal and abnormal human rod photoreceptors. Understanding rod receptor involvement in different diseases and in the normal process of light adaptation are among the specific aims of the proposed research. Our successful application of a quantitative model of the rod from the animal physiological literature encourages us to extent this work along two lines. First, we propose to measure cone a-waves and to compare them to models of cone receptor activity. In addition, alternative models of human cone receptor adaptation will be tested. Second, the long term goal of the proposed research is a quantitative model of the human ERG useful for testing hypotheses about normal and abnormal retinal activity. Thus, we propose to develop a model of the human ERG that encompasses the activity of the inner nuclear layer as well as the receptors.